A South Australian irrigation lobby group says both sides of politics need be more honest when talking about how the state will meet its Murray-Darling Basin Plan commitments.

Under the Plan, South Australia has committed to returning 183 gigalitres to the system, and the SA Opposition says there are questions about where the Government will find 20 gigalitres of that contribution.

Member for Chaffey, in the state's Riverland region, Tim Whetstone, says future contributions to the Basin Plan shouldn't come from productive water held by irrigators.

"We need to have a look further afield of the 183 gigalitres to date all of that has come through buybacks from irrigators or infrastructure upgrades, for the benefit of the Lower Lakes."

But the Minister for Water, Ian Hunter, says that's exactly what the government's doing.

"We already have programs that we're putting up to the Federal Government that need to be approved and funded, and they'll be progressed over the next five years.

"For the Opposition to demand to know the source of that water return right this very minute is impossible, because those programs are still in their early stages."

South Australia Murray Irrigators chair Caren Martin says the water will come from irrigators, and the discussion needs to be around how it's done equitably.

"The record needs be set straight. This water will be coming from irrigators and regional communities, because in South Australia, under the Federal Water Act, that's where the water can come from.

"The low-hanging fruit has been picked, and now we're looking at areas where people really value their water and want to keep it in their communities."